The present invention relates to new allergen-containing substances for use as immunologically specific suppressants of the production of reaginic antibodies directed to the allergen in question. The invention also relates to a method for preparing such new allergen-containing substances.
The present invention relates also to the use of tolerogenic conjugates of allergens with non-immunogenic, water-soluble polymers (such as polyethylene glycols) for the immunologically specific suppression of the common allergies of the "immediate type" in mammals including humans, which are mediated by reaginic antibodies of the IgE class.
About 15% of the population in developed countries suffer from allergies to apparently innocuous substances in their environment such as inhalants (e.g. pollens, dusts and feathers responsible for extrinsic asthma and hay fever), various foods, wool, drugs, etc. Allergic patients, as distinct from normal individuals, produce reaginic antibodies against the antigenic (allergenic) constituents present in these substances.
Generally the term "antigen" refers to a substance capable of eliciting an immune response and ordinarily this is also the substance used for detection of the corresponding antibodies by one of the many in vitro and in vivo immunological procedures available for the demonstration of antigen-antibody interactions. Similarly, the term allergen is used to denote an antigen having the capacity to induce and combine with reaginic antibodies; however, this definition does not exclude the possibility that allergens may also induce antibodies of classes other than IgE. As used herein, the term "antigenicity" is defined as the ability of an antigen or allergen to combine in vitro with the corresponding antibodies; the term "allergenicity" or skin activity as the ability of an allergen to combine in vivo with homologous reaginic antibodies thereby triggering systemic anaphylaxis or local skin reactions either in direct skin test or in passive cutaneous anaphylatic (PCA) reactions; and the term "immunogenicity" in a limited sense as the capacity of an antigen or allergen to induce the corresponding specific antibody response in vivo. The term "tolerogenicity" means the capacity of an allergen-containing substance to substantially suppress in vivo, in a specific manner, the immune response to the corresponding non-modified original allergen; in this context the term "tolerogenic" will be used interchangeably with the term "immunosuppressive".
Reaginic antibodies have the distinct property among all classes of immunoglobulins of becoming fixed to tissue mast cells and basophils of the individuals who actively produce these antibodies or of individuals into whom an allergenic serum is injected. The crosslinking of the IgE antibody molecules fixed to these cells by the appropriate allergen triggers the degranulation of these cells, which is followed by the release of pharmacologically vasoactive agents from their granules, e.g. histamine, bradykinin, the slow reacting substance of anaphylaxis (SRS-A), eosinophil chemotactic factor of anaphylaxis (ECF-A) and a platelet activating factor. These compounds lead to the allergic symptoms, i.e. the systemic or local inflammatory reactions, by acting on blood vessels and smooth muscle tissues; in severe cases these reactions may lead to anaphylaxis.
The currently used therapeutic procedure involves a lengthy series of injection of the offending allergen over many years, which has to be administered in minute doses because of the inherent allergenicity of the natural products and the consequent danger of their triggering systemic anaphylactic reactions.
Therefore, for a safe and effective therapeutic procedure it is essential to produce derivatives of the natural allergens which should be capable of acting as tolerogens by markedly suppressing, if not totally abrogating, the IgE antibody response in an immunologically specific manner. Furthermore, these tolerogenic derivatives should possess two additional properties, namely (i) they should be nonallergenic, i.e. they should be unable to combine in vivo with the IgE antibodies fixed to mast cells and basophils and, consequently, they should not be able to trigger anaphylactic reactions and (ii) they should be nonimmunogenic, i.e. they should not be capable of inducing an immune response to themselves on repeated injections.